The present invention generally relates to memory systems, and more particularly to a technique for the recovery of frame synchronization in dynamic, non-destructive memory systems. The invention is especially useful in the recovery of loop frame synchronization in a magnetic bubble domain mass-memory.
Magnetic bubble domains in soft magnetic thin films provide large-capacity information storage of high reliability at very low cost. Thin film magnetic bubble memories permit information to be processed in two dimensions and provide both non-destructive read-out and logic operations. A good general description of magnetic bubble domains and their potential applications is provided by Andrew H. Bobeck and H. E. D. Scovil in their article entitled, "Magnetic Bubbles" published in the June, 1971 issue of Scientific American at pages 78 to 90.
The present invention will be described primarily in terms of a bubble mass-memory organized so that a number of minor loops hold data and transfer the data on command into a major loop for read-out as described on Page 90 of the Bobeck and Scovil article. In such a memory, the magnetic bubbles are typically moved in the thin film by means of a rotating magnetic field acting in conjunction with a pattern of thin-films of Permalloy on the soft magnetic thin film and having special geometric shapes. One of the main advantages of a bubble memory of this type is that it is non-destructive as far as the data are concerned; however, loop frame synchronization usually depends on the information in the control hardware which is typically Large Scale Implementation (LSI) semiconductor circuitry. This circuitry is data-destructive in nature upon catastrophic failures such as power failures or the like. Recovery of the loop frame synchronization after a power failure, for instance, becomes an important problem if the data in the memory are to be usable.
One approach which might be used to permit resynchronization of the loop frame data is to assign a number of bits at the beginning of the frame as synchronization word or header block. Such a technique is typically used in digital communications. Although this would be a reasonable approach in loop recynchronization in bubble memories, each loop in the memory would require such a header block resulting in a space redundancy and requiring additional logic, making it unattractive, especially when the loops are not big in size.